Unique physical properties and an abundant supply have established asphalt as a major raw material for use in industrial applications that involve structural adhesive and waterproof protective films. The major markets for these industrial applications are road paving and roofing respectively. Both asphalt cement and mineral filled roofing asphalt can comprise a mixture of asphalt with silica or limestone based minerals. Consequently, chemical and physical factors which can influence the asphaltic coating of minerals are operative in both applications.
Residual oils and/or bituminous materials, such as asphalt, used in the preparation of pavements do not coat and adhere well to mineral aggregates unless the aggregate is substantially dry, and, for this reason, in conventional pavements it may be necessary to dry the mineral aggregate prior to blending with the bituminous material.
Mineral aggregates employed in road pavement range in character from hydrophilic to hydrophobic. In general, siliceous and acidic minerals, such as sands and gravels, tend to be hydrophilic while calcareous, alkaline minerals, such as limestone, tend to be more hydrophobic. It has been observed that the mineral aggregates appear to have a greater attraction for water than for oil or bitumens and that it is difficult to obtain complete or satisfactory coating of aggregates by oil or bitumen when water is present. Furthermore, even though satisfactory coating may be obtained by using dry aggregates, the oil or bitumen tends to be displaced if water enters the pavement or road.
One approach which has been used to decrease the severity of the problems attributed to poor adhesion between the aggregate and bitumens and/or stripping of the bitumen from the aggregate due to the presence of moisture has been to include an additive (hereinafter referred to as an antistripping agent) in the bitumen prior to combination with the aggregate. These anti-stripping agents serve to enhance the coating of the aggregate by bitumens and retard displacement of the aggregate-bitumen bond by water.
The art discloses several antistripping agents which are useful as additives in bitumens and asphalts. For example, U.S. Pat. No. 2,759,839 to Crews et al. discloses the use of certain amines as antistripping agents.
U.S. Pat. No. 3,985,694 teaches the use of terpenic resins and interpolymers of ethylene, methylacrylate and an organic acid improves certain properties of asphalt compositions such as adhesion to aggregates.
U.S. Pat. No. 3,867,162 discloses the use of tall oil as an adhesion promoter in bituminous emulsions.
U.S. Pat. No. 3,615,797 discloses the use of tertiary amines as bitumen additives which improve the adhesion properties of the bitumen. U.S. Pat. No. 3,978,014 discloses the use of bituminous compositions containing two polymeric materials; one which improves the resistance of the material to flow under elevated temperatures, and the second causes improved adhesion to other materials. The second polymer is characterized by having a molecular weight of at least 10,000, a solubility parameter (defined in Dutch Patent Application No. 6,706,408) of between 7.8 and 8.8 and a crystallinity of less than 60 percent at 25.degree. C. The second polymer is disclosed to include for example polyethylene, polybutadiene, chlorinated polyethylene, ethylene, ethylacrylate copolymers, ethylene vinylacetate and the like. The polymers must each be employed in a minimum amount of 4 weight percent of the composition.
U.S. Pat. No. 4,430,127 discloses the use of an expoxylated polyamine to provide adhesion between aggregate materials and the bitumen.
In copending application Ser. No. 817,659; filed Jan. 10, 1986, certain olefinic polymers are employed in an amount of at least 1 part by weight of an asphalt blend to provide improved characteristics at elevated temperature. The polymers are disclosed to have a melting point between 140.degree. F. and 350.degree. F. and a melt flow index of at least 50 g/10 min. The blend is disclosed to have improved stability, antistrip and solvent resistance properties.
U.S. Pat. No. 3,364,168 discloses a blend of low molecular weight, low density polyethylene, refined grade lube oil and petroleum resin provides a material which can be employed as road paving substance and the like.
The present invention is based on the discovery that improved adhesion of aggregate and bitumen can be achieved by incorporating small amounts of certain .alpha.-olefin copolymers into the mixture.